Session: General Posters:

Carbohydrates are the essential biomolecules of life as they form the forefront of interactions with receptors, proteins, pathogens, or neighboring cells. On cell-surfaces, carbohydrates are mostly found as linear or branched glycoconjugates, and a majority of them are linked via either 1,2-cis or 1,2-trans O-glycosidic linkages. The synthesis of 1,2-trans glycosides can be reliably achieved via the neighboring group assistance. The synthesis of axial 1,2-cis glycosides is more difficult because, beyond weak anomeric effects, there are no forces helping in directing the stereoselectivity. The synthesis of β-mannosides (equatorial 1,2-cis glycosides) is complicated further because the anomeric effect is working against it. Current methods for β-mannosylation require specialized donors and super-low temperatures.
Hydrogen-bond-mediated aglycone delivery (HAD) method introduced by our lab makes use of remote picolinyl and picoloyl groups that are capable of providing a strong stereodirecting effect. Among a variety of targets and substrates investigated, our lab determined that a highly stereoselective formation of β-mannosides can be achieved via the assistance of the remote 3-O-picoloyl group. Presented herein is the extension of the HAD method to the stereoselective synthesis of oligosaccharides containing D-mannosamine (ManNAc), D-mannuronic acid (ManA), and D-mannosamine uronic acid (ManNAcA). These residues are quite abundant in the microbial glycans, wherein they are typically connected via β-(1,2-cis) linkages. Also discussed is the development of complementary approaches to stereocontrolled α-mannosylation.

Catherine Alex

Graduate Student, University of Missouri, St. Louis

Appearances